1. Technical Field
The present disclosure relates in general to wireless communication devices and in particular to duplex filters in wireless communication devices.
2. Description of the Related Art
In multi-band handset designs, it is desirable to use separate antennas for the receive channel and the transmit channel in a given frequency band, as opposed to conventional or single-band designs in which the receive channel and the transmit channel share an antenna. Narrow bandwidth antennas are desirable because the physical antenna volume can be reduced. Having separate transmit and receive antennas allows utilization of narrower bandwidth antennas. Furthermore, having separate transmit and receive antennas enables the use of narrow bandwidth antennas since a given antenna matching state is utilized to provide good performance for only a transmit channel or a receive channel, during respective intervals. However, when a single shared antenna is utilized for both transmit and receive channels, the antenna's bandwidth must be determined based upon the receive and transmit channels and the guard-band in between the receive and transmit channels. Separate receive and transmit antennas require the use of “split duplexers”. In a split duplexer, the receive channel side and the transmit channel side of the duplexer are not connected as in a conventional duplexer but are electrically separated. The split duplexer can be utilized only for a limited number and specific type of transmission modes.